Ceramic pigment



Dec. 30, 1952 a. w. KING. JR.. Erm. 2,623,833

v cERAuIc PIGMENT med June so. 1949 2 sum'rs-sxmnz'r 1 Pf awr kanjer/wes u s a a l k I, z a s 40o Joa boo 70o 400 5w 60o 700 WMM/6TH /N mum/cnam NAVA-mam uv Munn/Cms JNVENTOR Dec. 30, y1952 a. w. KING, JR.. :TAL 623,833

CERAMIC PIGMENT Filed Juney 30, 1949 sHgETs-sl-IEET 2 PEA' cEN REFLEcrA/vcr f z 1 l 'JNVENToRl 0. ggr

wAvrLrNarH '1N MlLLlM/cRoA/J Patented Dec. 30, 1952 CERAlWIC PIGMENT Burnham W. King, Jr., Shaker Heights, and Adolph 0. Tesar, Cleveland, Ohio, assgnors to The Harshaw Chemical Company, Cleveland, Chio, a corporation of Ohio Application June 30, 1949, Serial No. 102,198

(Cl. S- 299) 4 Claims.

4(September l, 1932) suggests calcining ZrO2 or SnO2 with a small quantity of vanadium or molybdenum oxide at from 1100a C. to 1500 C. for the produ-ction of yellow pigments. This same patent suggests also the three component compositions resulting from the addition of small quantities of S102, Ti02, or A1203 to the ZrO2, vanadium oxide mixture. Earl (U. S. Patent 2,438,335)

has claimed good results from ZrO2 Iand V205 y when pure ZrO2 is used. He requires freedom from soda. The British patent is silent as to the degree of purity. The British patentee prefers to have silica or alumina present (in the order of 1%) while Earl does not use either. Seabright (U. S. vPatent No. 2,441,447) uses ZrO2, Si02 and V205, ammonium metavanadate or the like and obtains greens in the absence of alkali and blues when alkali is present. Seabright, however, works within proportion limits quite dilferent from those mentioned in the British patent.

It might be inferred from the literature that the colo-r exhibited by such pigments depends upon the valency state of the vanadium but we are not certain as to this. -The blue color obtained by Seabright might be explained asA a result of conditions rendering vanadiumstable in the tetravalent form and the yellows of the British patent (which our experiments indicate are poor pigments) might be explained assa result of conditions rendering vanadium stable in the pentavalent form. The green obtainedv by Seabright could then be explained as a stable mixture of tetravalent and pentavalent Vanadium. Such theories may or may not be eventually demonstrable but it is our experience that many compositions of the general types described in the above patents are of no value as ceramic pigments. If it can be assumed from his failure to mention it that the British patentee did not realize the excellence of color obtainable by the use of pure ZrO2, he was very close to the pigment of the Earl patent but failed to achieve the same quality. This may indicate how critical the production of an excellent pigment of this type Y and silicon and wherein ZrO2 is the principal' component. Like Earl, we found that a good'pig-Y ment was not obtained by simply calcning technical ZrO2 and V205 or ammonium metavanadate when the ZrO2 was contaminated with soda. We did not, however, favor the use of pure ZrO2 on account of its cost and sought to find other means of solving the problem. We have done considerable Work with a commercial type of ZrO2 ,(Opax) containing soda and silica. The soda is typically about 1% by weight as Na20 and the silicaruns about 5% by weight, percentages based upon the total Weight of the ZrO2 plus impurities on the analytical basis, but is mostly if not entirely present as a zirconium silicate. We did not secure a pigment capable of yielding a strong yellow by calcining this impure ZrO2 with V205 or ammonium metavanadate. V

We have discovered, however, that if we calcine ZrO2 containingfrom 0.2 to 2 of Na2O by WeightI and less than 5% of free silica, preferably less than 2%, by weight, with V205 or ammonium vanadate and Ti02, in suitable proportions and under suitable conditions, we do obtain a Ipigment capable of yielding excellent, strong yellow ceramic bodies or glazes (slightly browner than lemon yellow) in spite of the presence of such proportions of soda. The pigments themselves in powder form do not have the desired yellow color but are quite brown. In respect to free silica content, it should be noted that ZrO2 is usually derived from zirconium silicate and the silicacontent frequently is not free silica even though it might be inferred from the report of the analyst to be such. The manufacturer may give only the analytical report and so lead to the assumption that the silica content is free silica when in fact it is present as zirconium silicate or insome other tightly bound state of association rendering it unreactive. We have found, furthermore, that even in the absence of soda in the ZrO2, brighter colors are obtained by the use of ZrO2, V205 and Ti02 in the proportions indicated below. The titania used may be in either the rutile or the anatase form. lThus, whether the ZrO2 be pure or contain soda as `an impurity, there is a definite improvement Vin the use of T102 in properV proportions although the improvement is not as great in soda free combinations as in soda containing combinations. 0n a general basis, suitable proportions for essential components for realizing the benefit of Ti02 would be: ZrO2 60 to 90 parts by weight, V205 4 to 30 parts by weight :and T102 2.5 to 35 parts by weight. These proportions would be for the pigment and would also be the same for the preferred batch except that 4 to 30 parts V205 would be changed to 5.1 to 38.5 NH4VO3, although V205 can be used in the batch and other materials which upon calcination will yield the essential oxides are equivalent.

Using Opax, an impure ZrO2 containing 1.0% of NazO by weight and 5.0 per cent of unreactive Si02, suitable proportions are 60 to 9G parts by Weight of such technical Zr02, 4 to 30 parts by weight V205 (equals 5.1 to 38.5 parts by weight of ammonium me'tavanadate) and 2.5 to 35 parts by Weight T102. Within these limits, optimum proportions are 75 to 86 parts by Weight of such technical Zr02, 7 to 24 parts by weight of V205 (equals 9 to 34 parts by Weight ammoniummetavanadate) and 6 to 20 parts by weight of T102. This may be expressed in more completely descriptive fashion as 50.4 to 75.6 Zr02, 4 to 30 V205, 2.5 to 35 T102, 0.6 to 0.9 Na20 and9 to 13.5 ZrSiOi, parts by Weight respectively with optimum limits of Na20 0.7 to 0.85, ZrSiOi 11.2 to.12.9., Zr02 63 to 72, V205 7 to 24 and Ti02 6 to 20, parts by Weight. We are not, however, restricted to the one typeof technical Zr02 but may use others having varying amounts of Na20 and S102. Technical materials are availablev having from a trace to Na20. Formulations exceeding 2% Na (based upon `theweight o1 the pigment) are unsuitable for our purpose. Silica (unreactive) ymay vary from none to 5% or 7% of the nal pigment by Weight. It is difiicult to iind a source .of Zr02 having less than about 1% S102. Free S102 in the batch should not run more than 2% of the weight of the nal pigment. The use of these technical materials is not necessary to the results. The technical Zr02 containing soda and unreactive S102 can be replaced by highly pure Zr02 plus soda ash plus ZrSiOi in such proportions as to give the same calculated pigment compositions as the above stated proportion limits would require and when this is done, results are obtained which approximate those obtained with the technical materials. The results are vastly different when the technical materials are synthesized using free silica. The unreactive, type of silica seems, therefore, to be merely the silica component of ZrSi04 present in the technical materials. The batch, then, may contain Zr02, Na20, ZrSOi, S102 (free), V205 0I' NHiVOs, and T102 or materials which will yield these compounds upon ring; and they may be present in such proportions that the composition of the nal pigment will be approximately (parts by weight) Zr02 99.8 to 77 ZrSiO4 'G to 21 Nago 0.2 to 2.o 60 m90 S002 (xfree) 0 to.'` 5.0

Preferable proportionsfo'r optimum results, considering costs as well as results. in respect to the important impurities Na20, S102 and ZrSiOi. are approximately (parts by weight) 1 Without distinguishing the source of oxides.

from the batch., the nal pigment may essentially contain (parts by Weight) Zr02 99.8 to 98 Na2O 0.2 to 2.0} 60 to 90 V205 4 to 30 T102 2.5 to 35 This formulation omits zirconium silicate which is not a necessary component although usually present because of its presence as an impurity in the raw material. A preferable pigment composition, having regard, to costs and best limits of proportions would be (parts by weight) Zr02 96.8 to 93.5 S102 2.5 to 5 75 to 86 Na20 0.2 to 1.5 V205 7 to 24 T102 6 to 20 In the yaccompanying drawings, Fig. 1 is an lapproximate reproduction on a reduced scale of three spectrophotometer recordings on glazed tile showing the comparative eiects of the use of S102, A1203 and T102 in a Zr02-V205 composition used for coloring the glaze on the tile; Fig. 2 is a triangular diagram showingA suitable and optimum proportions of a technical Zr02, V205 and rE102 in the product (the Zr02 includ- ,ing Na20 and S102 in the above indicatedV proportions) ;Fig. 3 is a. view similar to Figl but showing the, eiect on a Zr02-V205-Ti02 composition (full line) of varying` the proportion of V205; Fig. 5 is a View similar to Fig. 3 showing the effect on such composition of varying the proportion of T102; Fig'. 5 is a similar view comparing the color characteristics in tile of the optimum composition O-T) With a similar composition omitting T102 (0), compositions having 5% of free silica with (5-T) and Without (.5) T102 and compositions having 15% of free silica with (l5-T) and without (15) T1102; Fig. 6, a similar view comparing two synthetic approximations of the best composition (Fig. 1, T102), the silica in S being freel as introduced into the batch and in Z being combined in'ZrSi-02; and Fig. 7 is a similar view showing the effect of adding to the best composition (0, Fig. 7) varying quantities of free S102.

In the production of pigments according to the invention, the batch is made up from suitable compositions which will break down into the above indicated oxides, or oxidize to the valence indicated, or the batch may be made up of the ultimate oxides themselves. A preferable source of vanadium pentoxide is ammonium metavanadate (NHG/03). Zirconium oxide is preferably added as such to the batch, but as indicated above, it may contain small proportions of soda and zirconium silicate as impurities and may even contain a small proportion of free silica. Ti02 is preferably introduced into the batch as such'.

The components of the batch, in finely divided or powdered form are thoroughly admixed and oalcined at a temperature ofl the order'of from 1100o C; to 1400o C. The kiln atmosphere may be neutralv or oxidizingv but should not be'reducing. The batch is placed in the kiln and brought up to the indicated temperature range and held therein for the desired period of time which may be from 1 hour to 8 hours or more, for example over night (about i5 hours) or even 24 hours, but there appears not to be any advantage in calcining for longer periods of time. Examples in the table below were calcined between 1100" C. and 1250" C. for about 6 hours, the temperature rising from 1105o C. to 1250 C. and falling again to 1100" C. in about that time. 1 to 8 hours'may be considered a 'practical time range, the heating time being varied in proportion to the size of the batch and the temperature. 'I Y The above indicated proportion ranges have been indicated graphically in Fig. 2, the outer sixsided gure within the large triangle indicating suitable proportions which are those numerically stated above, Iand the small four-sided figure vwithin44 the hexagonal iigure indicating optimum proportions numerically stated above. The limiting chemical Values have been placed on the drawing for convenience in view of the fact that the figure has been made on a small scale and. therefore, does not lend itself Well to placing .a series of cross lines to indicate the numerical values corresponding to the sides of the gures representing the proportion areas. It will be understood that distances from each sideV of the triangle toward the opposite angle indicate the proportion of the component indicated at the angle corresponding to any given point in the figure. This :accords with conventional use of the triangular diagram.

The curved lines in Fig. 1 illustrate the eiect of using titania, silica and alumina in a composition which otherwise is constant. For example, the full curved line marked TiOz indicates the color of a tile coated with a glaze colored by a strong pigment in accordance with the invention, the composition being that of sample 1 in the table below, and the other two curved lines indicate the results of pigments made by substituting for the titania, equal weights of alumina and silica. In other words, the T102 curve resulted from a batch made up of 95 parts by weight ZrOz, 15 parts by weight ammonium metavanadate and parts by weight TiO2. The A1203 curve resulted from a batch made up of 95 parts by weight ZrOz, 15 parts by weight ammonium metavanadate and 10 parts by weight A1205 and the SiOz curve resulted from a batch made up of 95 parts by weight ZrOz, parts by weight ammonium metavanadate and 10 parts by weight SiOz. In these instances the ZrOz contained approximately 1% NazO and approximately 5% SiOz in the form of zirconium silicate. (That is, the ZrOz was only about 84% ZrOz, 1% NazO and 15% ZrSiOi.) The full line represents a strong yellow color slightly browner than lemon yellow. The AlzOz line represents a weaker yellow color while the SiO2 line represents a greenish color. We do not fully understand the reason for this different behavior of these materials, but numerous trials have been made and these results have been found to be characteristic.

A number of runs were made for the purpose of determining the eect of varying the propordicated by the numeral il." indicates the color in glaze on tile resulting from a batch containing 95 parts by weight ZrOz of the same kind used in connection with the compositions of Fig. 1, 15

plied to this type of pigment.

In Fig. 4, we have shown in full line, labeled I0, the color in glaze of a pigment which resulted from a batch composition identical with those indicated by the full lines in Figs. l, 3, 4, 5, and 7. (Application of the glaze to tile, ring and other conditions vary slightly and give slightly different curves even from the same composition.) This curve resulted from a batch made up of 95 parts by weight of the same type of ZrOz used for the previous examples, 15 parts by weight of ammonium metavanadate (11.7 parts V205 calculated) and 10 parts of TiOz. In reducing the amount of 'IiOz to 3 parts instead of 10, a paler yellow was produced, the color of which is indicated by the dashed line 3. Going to the other extreme and using parts of TiOz, a tile was produced having the color indicated by the dot and dash line 50.

Several other compositions in the series of Figs, 3 and 4 were tested but it was thought better not to confuse the drawings by an excessive number of lines; they showed intermediate color characteristics. It was found that the compositions represented by the full lines in Figs. 1, 3,

parts by weight of ammonium metavanadate and l0 parts by weight of TiOz. Leaving the other factors constant, the amount of ammonium metavanadate was varied both above and below that represented by the full line. It will be understood that 11.7 is the calculated amount of V205 resulting from 15 parts by weight of ammonium meta- 4, 5 and 7 are those which give the strongest yellows.

The addition of free silica to the composition giving the strongest yellow was found to result inl a greenish coloration. Inasmuch as the com-r position indicated by the line TiO2 in Fig. 1 was found to give a strong yellow free from the greenish effect, the conclusion was reached that the technical ZrOz which the analyst reported to contain about 5% of silica either did not contain any such quantity of free silica or else the TiOz content was capable of suppressing the tendency toward the green coloration. Both factors were found to contribute to the result. That is, when free silica was present, the presence of titania was effective to reduce the tendency toward greenish coloration, and it was found that the SiOz reported by the analyst in the technical ZrOz did not behave in the same fashion as free silica 'out behaved like zirconium silicate. On the assumption that the silica reported by the analyst was in the form of zirconium silicate, and be'- cause no analytical methods were available to distinguish between silica in the free state and silica combined in zirconium silicate, the com# position represented by the line TiOz in Fig. 1 was synthesized roughly on two assumptions, one that it was free silica and the other that it was combined in zirconium silicate. By reference to Fig. 6 and samples 15 and 16 in the table below the results will be seen. The line Z in Fig. 6 indicates'the color resulting from the composition of sample 16, while the curve S resulted from the composition of sample 15. It will be seen that the calculated pigment composition is the same in each case but that a relatively pure ZrO-z was used and the 5% silica content was supplied in the one case as free silica and in the other case as zirconium silicate, the ZrOz content being reduced by Ithe'ainount of ZrOz;addedjas'zlrconium silicate'. The result of this comparison. isv striku ing, the. greenish coloration being very marked in theA case of the composition containing free silica and a good yellow resulting fromthe, other composition, although not as good as the. composition corresponding to the line TiOz` of Fig. l. This may be accounted for partly by the fact that the supposedly pure ZrOz was not entirely free from silica but, contained 0.8% SiOz on the analytical basis and .2% of lime. It is, however, suiciently close to indicate thatl the amount of free silica in the ZrOz is small if there is any at all.

An extension of this test is shown in Fig. where three pairs of compositions were compared, each diifering from the other member of the` pair by the fact that Ti02 was included or not. In Fig. 5 the thin, full line il contained no. titania, whereas the heavy full line tl-T was the same except that it contained ten parts of. T102. The line ll-T represents the same composition; as that indicated by the line TiOz of.' Fig. 1 and may be referred to as the best composition. It will be seen that by omitting the titania the reilectanoe was increased in the blue endV of the spectrum and decreased in the red. This weakens the reddish factor while increasing the bluishness. This, in the case of a yellow pigment gives the effect of moving toward the green. Also, it approaches closer toward what would be gray and gives the effect of a paler yellow. in the case of these two compositions, the appeal to the eye is more of a paler yellow than of a greenishness. In other words, these two are close enough that the un trained eye does not detect a color recognizable as green but sees a somewhat paler yellow. Changing these two compositions by the addition of ve parts of SiGz, as seen in the table below, we produced compositions yielding colors as indicated on Fig. 5 by the color curves labeled 5 and 5-T. Here it will be seen that the silica has in each case contributed to an increase in the blue end of the spectrum and a fairly sharp decrease in the red. Similar curves adding l5 partis of.' SiOz produced colors corresponding to thev curves l5 and IIE-T. Here the hook in the red end of the spectrum is very pronounced and the blueness is further increased. The tiles from whichthe color curves I5 and I-T were taken are distinctly greenish and may be characterized as brownish green.l The greenishness in the case of curves 5 and -T is distinctly perceptible. By comparing the members of each pair of curves in Fig. 5, itwill be seen that the tendency toward greenishness is markedly reduced by the presence of TiOz. Thus, absence of free silica and presence of titania are both important in the production. of a good strong yellow of the character indicated.

The series of curves shown in Fig. '7 was made for the purpose of determining how much free silica can be tolerated in ZrOz-VzOs-TiOz compositions according to the invention. The sample labeled 0 in Fig. '7 contains no added SiOz and corresponds to the composition labeled TiO2 in Fig. l. Adding two parts of SiOz, which figures 117%' SiOz in the pigment derived from free SiOz, a tile was produced having the color indicated by. the dotted line labeled 2. It will be seen that acterized as a good yellow color; Increasing-the S102 content to threeparts, which calculates to 2.5% SiO2 in the pigment derived from free SiOz, there was produced a tile yielding a color represented by the color curve labeled 3 in Fig. '7. This exhibits about the same deficiency in the red end of the spectrum as the composition corresponding to the line il but shows substantially increased reflectance in the blue end of the spectrum. This composition is not characterized by the same excellence as the preceding one but might still be called fair and might be preferred for some uses. Going on to the color curves representing compositions to which increasingly larger quantities of silica were added, these are found in Fig. 7, each labeled with the number of parts of SiOz added to the best composition. The compositions containing 0 and 1.7% SiOz derived from free SiOz might be termed excellent a1- though the one containing no added free SiOz is distinctly the better of the two. The compositions containing and 4.1% silica in the pigment derived from free S102 might be said to be fair while those containing larger quantities have become distinctly greenish. From the color lines in Fig. 7, itcan oe seen quantitatively how each increase in added silica progressively reduces the strong yellow color characteristic.

Assuming that the use of pure ZrOz is not practicable from cost considerations and particularly that soda must be tolerated in order to make possible the use of technical ZrOz which can be had at a favorable cost, it has been found important to select materials containing little or no free silica. It has been found. that unreactive SiOz combined in zirconium silicate can be tolerated and that, while distinguishing between Vfree silica and silica in the form of zirconium silicate is difficult if not impracticable by ordinary analytical methods, the reactive silica content of ZrOe raw materials can be tested by the determination of the color characteristics through the medium of the recording spectrophotometer as applied to test tiles. For good results, raw materials containing free silica should be excluded if possible and those resulting in more than 2% of silica in the pigment composition derived from free silica in the batch should be rejected. Soda can by tolerated up to 2% on the basis of the nal pigment weight and, having in mind cost considerations, apparently must be tolerated to a substantial extent. It is, of course, an important feature of this invention to make possible the toleration of soda to theV extent that relatively cheap technical raw materials can be used and still produce a pigment capable of yielding a strong rich yellow coloration for ceramic uses. Thev fact that the pigment itself approaches a chocolate brown color is not of great importance so long as the color in tile possesses the desired characteristics.

It has been found that these brown pigments (which impart desirable yellniT colors when fired), and which it will be noted are in composition somewhat similar to those described in U. S. Patent 2,441,447. may be mixed in all proportions with the blue pigments described in that patent to give a whole series of very eective col,- ors ranging from the yellow of this invention through green to the blue of the compositions of that patent. This providesa very excellent range of yeliow-green-blue pigments which are brilliant throughout the entire range.

We are not certain of the state of combination, chemical or physical, of the constituent oxides 2,623,833 y 10 in the final pigment. Accordingly, the pigments the components; but such expressions do not will be defined in the claims as containing cersignify that in such compositions such oxides are present in the free state, nor do they signify anything concerning the state of association of such 5 oxides in the compositions defined. The expression compounds capable of yielding followed by a list of compounds, is intended to include compounds which when fired under the conditions claimed without the other components oi1 results in porcelain enamels but the percentage '1U the batch, would yield the indicated compound; e. g., NH4VO3 would yield V205, and V205 would yield V205.

In the following table we have shown a considerable number of examples of batch compositions according to the invention, together with the calculated final composition of the calcined pigment, it being understood that in all these batch compositions, except where pure zirconium oxide is speeied, the ZrO2 probably contained parts borax, by weight. Ceramic bodies are less 20 about 17% of Soda (NasO) and 5% 0f Silica tied up as Zircon although these values are only approximate and some variability is to Vbe expected as in any technical material. The Zr02 denoted as pure in the table was only relatively so, conand the 1ike expressions denote an 5 taining a trace of soda and about 0.8 per cent SiOz on the analytical basis, likewise subiect to some variation.

tain constituent oxides without thereby intending to signify anything concerning the state' of association of such oxides in the product. v

These colors are especially suitable for glaze and body stains and are also suitable for use in engobes, underglaze and overglaze stains and glass enamel colors. They give quite pleasing of pigment required in the case of porcelain enamels would increase the cost and tend to discourage their use in the low priced field. The invention is applicable to glaze and body compositions quite generally, suitable glaze compositions 15 being low melting glasses essentially alkali aluminum silicates with or without lead, for example, 43.3 parts feldspar, 18.5 parts Whiting, Y 25.3 parts iiint, 10.3 parts Florida clay and 2.1

glassy but otherwise similar, for example, clay 50%, feldspar 25% and flint 25%, by weight.

In the claims, the expression essentially consisting of oxides of zirconium, vanadium and titanium, analysis in terms of oxides of the elements, indicating a composition wherein such oxides are BATCH COMPOSITION (PARTS BY WEIGHT) ZrSiO4 i zroi (pmeS Ti0z.

=weak yellow; GY=greenish yellow; E=good yellow; BG= brownish green. l ZrOg was used in the batch, the ZrOz in the batch composition is about 1% NazO analytical basis, little or none ofthe S107 being free. The eiect of this is shown in the calculated compoe drawings to in two Iigures of the drawings; the upper reference character shown in the bottom line of this table =strong yellow; WY *In samples which do not indicate that pure ding the lines. Samples 14, 19, and 22 appear refers to Fig. 5 in each of these cases.

Nora-SY Samples 7 and ll were made and the color curves were intermediate adjacent samples but were omitted from th Color in glaze on tile. Labeled on drewings and 5% SiOz by weight, sition.

avoid overcrow Having thus described our invention, what we claim is:

l. A brown-ceramic pigment of the ZrO2-V2O5 type, wherein the ZrOz contains as an impurity from 0.2 to 2.0 parts by Weight of NazO based upon the weight vof ZrOz (impurities included), said pigment being capable of imparting to ceramic bodies a pleasing yellow color upon firing, such pigment being improved with respect to color by the inclusion of TiO'z therein, such improvement consisting in a lowered vreiiectance of light of Wavelength in the blue end of the spectrum and an increased reflectance of light of wavelength Vin the red end of the spectrum, the

said pigment essentially consisting of (parts by 1 weight) m02 99.8 to 95 Na20 0.210 2 0} 60 to 90 V205 4 to 3o T102 2.5 to 35 '2. AA brown ceramic pigment of the ZrOz-VzOs type, wherein the ZrO2 contains as an impurity 'from 0.2 to j2;0 `parts by'weight of NazO based upon the weight of Zr02 (impurities included), said Vpigment being capable of imparting to ceramic'bodies a pleasing yellow color upon ring, such pigment being improved with respect to color by the inclusion of TiOz therein, such improvement consisting in a lowered reflectance of t light f wavelength in the blue end of the spectrumand an vincreased reflectance of light of *Wavelength in the red end ofthe spectrum, the

isaid pigment essentially consisting of (parts by weight):

ZlOz .96.8.1)0 93.5 S192 2.5 t0 '5 V'75 12086 NafzO {L2-110 -l.5 V205 7 t0 24 T102 6 130720 1'2 ving not more than 21,parts by lweight of zirconium silicate fand not more `than5 'parts by weight free SiOz also based upon the total weight of said impure ZrOz, said mixture being capable of yielding a pigment of the `following composition (parts by weight) Zr02 99.8 to '77 ZrSiO4 up to 21 Nazo 0.210 2.o to 9 SiOz up to 5.0

V205 -4 to30 TiOz v2.5 t0'35 4. Process of preparingfrom impure zirconium oxide and compounds of Vvanadium and titanium ceramic pigments vcapable of imparting to ceramic glazes and bodies a yellow color of slightly 'brownish character comprising .calcining between 1l00 C. and 1400 C. for not less than one hour under non-reducing conditions a mixture .of compounds comprising an impure ZrOz containing as an impurity combined sodium equivalent to from 0.75 to 1.5,parts'by Weight of NazO based upon the total weight of said Zr02, such impure ZrOz containing from 10 to 15 parts by Weight of 'zirconium silicate and from 1 to 2 parts by weight `free SiOz also based upon the total weight of said impure ZrOz, said mixture'being capable of yielding a pigment of the following composition (parts by weight) REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number `N ame Date 2,213,168 Monk et al Aug. 27, 1940 2,441,447 Seabright May 11, 1948 FOREIGN PATENTS Number Country Date Great Britain Sept. 1, 1932 

1. A BROWN CERAMIC PIGMENT OF THE ZRO2-V2O5 TYPE, WHEREIN THE ZRO2 CONTAINS AS AN IMPURITY FROM 0.2 TO 2.0 PARTS BY WEIGHT OF NA2O BASED UPON THE WEIGHT OF ZRC2 (IMPURITIES INCLUDED) SAID PIGMENT BEING CAPABLE OF IMPARTING TO CERAMIC BODIES A PLEASING YELLOW COLOR UPON FIRING, SUCH PIGMENT BEING IMPROVED WITH RESPECT TO COLOR BY THE INCLUSION OF TIO2 THEREIN, SUCH IMPROVEMENT CONSISTING IN A LOWERED REFLECTANCE OF LIGHT OF WAVELENGTH IN THE BLUE END OF THE SPECTRUM AND AN INCREASED REFLECTANCE OF LIGHT OF WAVELENGTH IN THE RED END OF THE SPECTRUM, THE SAID PIGMENT ESSENTIALLY CONSISTING OF (PARTS BY WEIGHT): 